Help needed with linear bearings and hinges

I'm going to be honest, I have no idea what I am doing, at least with the things I'm asking help on.

I'm designing a sword with mechanical parts. The blades need to sit on a linear bearing to slide in and out. As well I need to either make or buy hinges for other parts. Attached is two models from a sketchup file, one open and one closed. If you have sketchup you can just import them. Also, there are two pictures of the linear bearings if you just want to look at those.

View attachment sword closed.zipView attachment Sword opend.zip

In the model Green is the two linear bearings, red and yellow are two different types of hinges that I'd like to be able to buy, and blue is the hinges that I think the 4 inch hing at lowes will work just fine (since its not really a load bearing hing I don't have to worry). The CAD is just a rough idea at this point. I need more info on the linear bearing and hinges to really hammer down the details.

The trouble is with the linear bearings mostly, again I have no idea what I am doing, so if anyone can help me determine what type or how strong I need it would be helpful, or just point me to any sources I can use to figure this out. The hinges are more just if anyone knows what type I could buy or what would be the best way to make them.

I've done some woodworking before so designing and building are not completely foreign to me, I just have no clue about details like what type of linear bearing is needed strength wise.

Thanks a lot for any help, and if this is the wrong thread for this can you just point me in the right direction.

Does this sword need to actually function as a sword or is it a cosplay prop?. That design is going to be really weak if there is only linear bearings down the bottom of the blade. There are lots of videos on YouTube with similar sword projects that would give you some good ideas on construction. Maybe a parallelogram pivot will be a lot more rigid and can also be made electrically insulated to allow the energy blasts to be channelled effectively up the middle of the blades.

Yes the blade needs to be functional, so strength is a must. The parallelogram pivot is an interesting idea. I was hoping to keep the blade movement linear, but it might be fine if it goes up then down back to being in-line horizontally with the first position. It only needs to travel 1.25 inches. The forces I'm most worried about are the straight up/down forces (relative to the models and pictures), so perhaps a parallelogram pivot with matching rods on both sides of the blades would work well, paired with a locking mechanism at each resting point.

I haven't nailed down how I'm going to mechanically separate the swords yet, I've got like three designs right now (one included in the models attached) so I'm more working on the structural stability of it right now. But I like that idea.

And yes, energy blasts are a factor

Austin.clayton said:

Yes the blade needs to be functional, so strength is a must. The parallelogram pivot is an interesting idea. I was hoping to keep the blade movement linear, but it might be fine if it goes up then down back to being in-line horizontally with the first position. It only needs to travel 1.25 inches. The forces I'm most worried about are the straight up/down forces (relative to the models and pictures), so perhaps a parallelogram pivot with matching rods on both sides of the blades would work well, paired with a locking mechanism at each resting point.

I haven't nailed down how I'm going to mechanically separate the swords yet, I've got like three designs right now (one included in the models attached) so I'm more working on the structural stability of it right now. But I like that idea.

And yes, energy blasts are a factor

Click to expand...

With the parallelogram pivot, the blades will stay parallel at all times, there just a bit of up and down movement as well, also if the parallel arms are widely separated, say 4 inches or so, the blades should be fairly rigid. A good tight fit for the pivots will be critical to making it work well. You could mount a battery drill motor in the pommel of the handle to drive a threaded rod up the handle that moves a nut/collar up and down the hilt of the sword to raise and lower the blades and provide the locking in whatever position it opens/closes at.

The movement up or down was what I was talking about, it may prove tricky with the designs I have now. However, I could just drop the hinges I was planing to go in between the blades that would do the opening and closing, actuate it down in the guard, and just have some type of locking bar that engages and maybe the mid and top part of the blade to keep it rigid and transfer force straight across and not down at the pivot when its open and chopping. I think I can only manage 2.5-3 inches for the arm separation (another good tip, thanks) with the space I have available in the guard. I'll sketch it out in CAD and see how it goes, it may even get rid of the need of those other hinges (especially the yellow ones). Thanks

The up and down movement also lends it to being operated by a linear actuator along the axis of the blades too.

You'll probably have to make some test pieces in easy to work materials like wood or plastic to get the hang of the joint function. nothing beats a physical scale model to test the concepts and spot flaws before committing to the real thing. I can only see the two images with the green slides, not the ones with yellow parts...must be the zip files.


Another mechanism that may work would be to use a "scissor jack" type. It can have a left hand and right hand screw thread for faster opening but robbing a cheap car jack and trimming to size would be the way to go. The only downsize I can see to either of the mechanisms is the risk of crushing a finger or even cutting one off if the mechanisms aren't adequately covered to prevent fingers from inadvertently getting between things. Picture this unit made smaller and stood on it's side to provide an automatically locking sideways actuation.

Austin.clayton said:

The movement up or down was what I was talking about, it may prove tricky with the designs I have now. However, I could just drop the hinges I was planing to go in between the blades that would do the opening and closing, actuate it down in the guard, and just have some type of locking bar that engages and maybe the mid and top part of the blade to keep it rigid and transfer force straight across and not down at the pivot when its open and chopping. I think I can only manage 2.5-3 inches for the arm separation (another good tip, thanks) with the space I have available in the guard. I'll sketch it out in CAD and see how it goes, it may even get rid of the need of those other hinges (especially the yellow ones). Thanks

Click to expand...

This project is way to ambitious for your skill level. You should start with something far more simple and work up to complex designs like this one. You are setting yourself up to fail instead of win.

No offence John Welden, but I'm here for some help in the design process, not to be talked out of it. Also, I'm not the one thats going to be making it, just designing.

A test piece is a good idea, I can do wood no problem (I do have the skill level for that).

Austin.clayton said:

No offence John Welden, but I'm here for some help in the design process, not to be talked out of it. Also, I'm not the one thats going to be making it, just designing.

A test piece is a good idea, I can do wood no problem (I do have the skill level for that).

Click to expand...

Please come back and show us the finished product and prove me wrong.

This jack would provide locking, sideways movement and keep the blades parallel all in one mechanism (fast forward to 5:49 to see it in operation):

Sorry, I didn't see the second half of your earlier post SAG 180. The scissor jack does look like a good rigid mechanism for spreading the blades, especially if it was to go in a groove in the blade to be use to spread it out. It would have to be very thin but would be very rigid. My only complaint would be the action required to actuate the mechanism. I'm looking for a smooth single action to do everything. I'm looking at maybe a handle (separate from the sword's handle) that could rotate around 90 degrees being used to actuate everything. I think would be great if I could get it to work with it. But I'll take the scissor jack into account and see if I can come up with something.